This work reported the synthesis of magnetic 5-9 nm NiFe2O4 nanoparticles for catalytic aquathermolysis of heavy oil using a straightforward solvothermal approach, followed by an analysis of the catalyst structure using several characterization techniques. Under the optimal conditions (240 degrees C, 24 h, 50 wt%, 0.1 wt% Cat.), the degree of viscosity reduction might be as high as 76.31 % when compared to the original oil. Additionally, 7.83 % of the heavy components (asphaltene 1.35 % and resin 6.48 %) are capable of being effectively converted to light components. The asphaltene is highly affected by the catalyst which results in lower S content and N content. In addition, the catalyst was subjected to a service life test, which showed a sharp decrease in catalytic performance after three cycles. Using several model compounds, an experimental investigation was conducted into the mechanism of heavy oil catalyst aquathermolysis. The aquathermolysis reaction broke the C-S, C-N, C-O, and C-C bonds in the heavy oil and decreased the viscosity of the heavy oil, according to the results of the GC-MS analysis. Our research offers a low-cost, highly effective option for catalytic aquathermolysis-induced viscosity reduction in heavy oil.